Source Tracking and Functional Prediction of Microbial Communities in Initial Jiupei of Fen-Flavor Baijiu: Daqu-Dominated Sourcing with Measurable Environmental Inputs

Understanding the microbial origin of initial fermentation grains (Jiupei) is important for improving process consistency in Fen-flavor Baijiu, yet the relative contributions of Daqu and the production environment remain insufficiently resolved. In this study, high-throughput sequencing, community ordination, SourceTracker analysis, co-occurrence network analysis, and PICRUSt2-based functional prediction were used to characterize the bacterial and fungal communities in initial Jiupei (JP0d), Daqu, and representative environmental reservoirs. Daqu was inferred as the dominant source, contributing 87.1% of the bacterial and 90.1% of the fungal communities. Environmental reservoirs provided smaller but detectable inputs: fermentation-room air (FJSKQ) contributed 2.53% of the bacterial community, equipment surfaces accounted for 1.1–5.1% of the bacterial community, and tools (GJ), cooling conveyors (LSJ), and distillation surfaces (ZT) accounted for 1.5–3.2% of the fungal community. The JP0d–JP28d correlation was higher for bacteria (r = 0.46) than for fungi (r = 0.39), indicating greater end-point compositional similarity for bacteria in this dataset. Functional prediction identified prominent pathways related to amino acid and carbohydrate metabolism, membrane transport, translation, replication, and repair in the JP0d bacterial community. These results support a Daqu-dominated source model for the initial Jiupei microbiota and indicate that the production environment may serve as a supplementary microbial reservoir in Fen-flavor Baijiu fermentation. The findings provide a microbial traceability framework for managing open solid-state fermentation systems.